Medical devices such as pacers and defibrillators connect to one or more lead assemblies that carry an electrical signal to or from a location of the body. In some instances, a lead assembly is inserted into the heart and fixated in a heart wall. In some devices, a fixation structure, such as a barb or helix, is used to fix to a tissue surface. A fixation helix may be screwed into a heart wall, for example. When inserting a fixation structure such as a fixation helix into a tissue wall, it is desirable to avoid perforation of the wall with the lead body, i.e. to avoid creating an excessively thinned area or a hole in the tissue wall.
In other instances, a lead assembly is fixated in a vessel, such as a blood vessel. For example, a lead assembly may be fixed in a coronary vein to allow pacing, sensing or delivery of therapies. Lead assemblies may also be fixated in other blood vessels or other locations.